Note that this is my opinion only, I am not a mechanic by trade.

Shutting off the engine via the key doesn't work on a diesel engine, as it does not have an ignition system, eg., no spark plugs, like your car engine does. As long as it has fuel, it will continue to run. Pulling the 'kill engine' handle, interrupts the fuel flow, stopping the engine. With the key off, the low pressure fuel pump is stopped, so eventually, I'd think the engine would be starved of fuel and stop.

The alternator diodes may be damaged if you switch your batteries off while the engine is running; this causes an open circuit on the load side and the diodes can be fried. However, I believe the stock alternators are more or less automotive alternators, and have an internal voltage regulator, which should prevent damage if the batteries are disconnected; I'd still not try it. But turning off the key should cause power to the alternator's exciter coils to be interrupted, so there would be zero output, hence no damage. I've had well meaning people turn off the key several times over the years with no damage; and I have a system with an external regulator and high output alternator.

Fully charged batteries should read somewhere around 12.8 volts. Under charge, maybe a volt more, depending on how much the alternator is putting out.

As to cranking for 5 seconds before starting. In my opinion, the only time you could do this is when the engine is cold, otherwise, it's just going to start. Diesel oil itself is a lubricant, plus the oil leaves a film on the cylinder walls. If the engine had been sitting for a [I]very[/I] long time; like months, I might want to crank it a bit first, but I'd not be worried otherwise. First start after winter storage, I usually give it a few seconds of cranking, then hit the preheaters for a count of 10 and it starts right up.

As far as I can see, you should be fine :) Again, I'm not a diesel mechanic, but the above is my understanding.

For whatever it's worth, I always turn the key off and then pull the decompression valve in short order. Been doing it like this for 25 years on Catalinas and nothing has broken yet (knock on teak).

Mike

[QUOTE=dejavu;5447]For whatever it's worth, I always turn the key off and then pull the decompression valve in short order. Been doing it like this for 25 years on Catalinas and nothing has broken yet (knock on teak).[/QUOTE]

Mike, that's not a decompression lever, it is a stop engine function, tied into the forward starboard upper side of your engine, just below the throttle connection. The decompression lever is on the top aft end of the engine. They are two separate items. See the blowup of the engine at [url]www.marinedieseldirect.com[/url]

For the OP : The key switch only activates the ignition and the gauges. You can turn it off even when the engine is running and the engine will continue to run.

It has nothing to do with alternator output except the field wiring, so when you turn your switch off it tells the regulator to tell the alternator to minimize / reduce / eliminate the output, set it to zero. This is all done through the regulator, whether internal or external. It does NOT interrupt the alternator output, which is defined as the physical wire and circuit from the + of the alternator to the battery +. There should be no damage to the alternator if the regulator does this. If, however, you interrupt the actual alternator output (physically or with a switch), you run the risk of damaging the diodes.

I recall a question just like this being posted recently. Perhaps on another board. In any event, suggest you do some more reading on boat electrical systems to get a handle on how your system actually does work and the difference between regulator signals TO the alternator and the alternator OUTPUT itself. A good place to start is the Ample Power Primer, click on the Tech Documents tab, here: [url]www.amplepower.com[/url].

[QUOTE=plaineolde;5444]

1. However, I believe the stock alternators are more or less automotive alternators, and have an internal voltage regulator, which should prevent damage if the batteries are disconnected; I'd still not try it.

2. But turning off the key should cause power to the alternator's exciter coils to be interrupted, so there would be zero output, hence no damage.

3. As to cranking for 5 seconds before starting. In my opinion, the only time you could do this is when the engine is cold, otherwise, it's just going to start. Diesel oil itself is a lubricant, plus the oil leaves a film on the cylinder walls. If the engine had been sitting for a [I]very[/I] long time; like months, I might want to crank it a bit first, but I'd not be worried otherwise. First start after winter storage, I usually give it a few seconds of cranking, then hit the preheaters for a count of 10 and it starts right up.
[/QUOTE]

1. Disconnecting the batteries WILL damage the alternator. If the alternator output is interrupted in any way, the diodes could fry. This includes turning the 1-2-B switch off. But not the key switch at the cockpit panel.

2. Correct

3. The glow plugs should be used any time you're starting a cold engine. The glow plugs should be used for 15 seconds if you have (added) a solenoid for the glow plugs circuit (for older M25 series engines; the newer engines have this handy feature built-in) or 30 seconds without it.

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If you want to turn over an engine without it starting, just pull the stop lever handle up (or at the engine) and keep it up and push the start button. Why would you want to do that?

Bill,

I might have and might now have hurt your alternator. Since you have a newer replacement yanmar engine I cannot comment 100% positively, but I can tell you on my 1999 C36MKII (#1800) with a Universal M35B that Catalina or Universal/Westerbeke must have installed some sort of 'failsafe' system in my boat because I have mistakenly turned off the key at the helm without shutting off the engine dozens and dozens of times and have not blown out my alternator. I think Stu explained why ...

Tom